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Abstract

A case of malignant mesenchymoma of the bladder containing leiomyosarcoma, rhabdomyosarcoma,
chondrosarcoma, osteosarcoma, and myxomatous components is described. The primary
pedunculated tumor measuring 14 × 13 × 7 cm and weighing 343 g arose from the left
trigone of the bladder and was treated by total cystectomy. The histogenesis of malignant
mesenchymomas and their optimal management strategy and prognosis remain uncertain.
Herein, we present the fifth case of malignant mesenchymoma of the urinary bladder
to be reported in the literature, which presented five unrelated differentiated tissues
more than did previously reported cases.

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Background

Malignant mesenchymoma, which was described by Stout in 1948, is defined as a malignant
soft tissue tumor that consists of two or more distinctly different mesenchymal components
in addition to fibrosarcomatous elements. A review of the literature revealed only
four cases of bladder sarcomas that fit the criteria.

Case presentation

A 77-year-old Taiwanese man had a multiyear history of symptoms of micturition difficulty.
Gross hematuria with severe pain had developed suddenly in the previous month. The
patient is a retired military soldier had neither history of cigarette smoking nor
habbit of alcohol comsumption. He had a history of hypertension and type II diabetes
mellitus for 20 years controlled with regular medication. He didn't exposures to paint
components or eat undercooked meat. There is no specific illness could be traced from
the patient's family pedigree. On physical examination, the patient appeared to be
recently poorly nourished and had normal vital signs and mild elevated blood pressure
at 151/88 mmHg. His lungs were clear, heart sounds were normal, and the abdomen was
soft, with no masses and no tenderness. There was no edema of the legs. In laboratory
data, the results of a complete blood count and the levels of electrolytes were normal.
However, serum total protein, albumin, creatinine (Cr), urea nitrogen (BUN), and glucose
were abnormal and showing hypoproteinemia (5.5 g/dL), hypoalbuminemia (3.0 g/dL),
abnormal renal function with moderate azotemia (BUN/Cr = 36/1.3), and hyperglycemia
(179 g/dL).

Real-time sonographic evaluation of the abdomen showed increased echogenicity of bilateral
kidneys. The sizes of the kidneys were 9 cm on the right and 10.3 cm on the left.
Mild dilatation of left renal pelvis is also noted. Furthermore, one lobulated mass
with urinary bladder wall thickening was also identified.

Magnetic resonance imaging (MRI) of the pelvis demonstrated a large mass in the urinary
bladder. The mass shows focal contrast medium enhancement on the left side with adjacent
vesical wall thickening and obliteration of the lower signal intensity on T2WI (Figure
1A). Urinary bladder malignancy was suspected, and the differential diagnoses included
urothelial cell carcinoma with blood clot, sarcoma, or other benign neoplastic mass.

Figure 1.(A) Magnetic resonance imaging (MRI) of the pelvis demonstrated a large mass in the
urinary bladder that shows focal contrast medium enhancement on the left side with
adjacent vesical wall thickening and obliteration of the lower signal intensity on
T2WI. (B) Macroscopically, the urinary bladder contained a nonencapsulated, huge, and
lobular mass, which was located in the left trigone and measured 14 × 13 × 7 cm in
size. (C) and (D) On the cut surface, this tumor was composed of a predominant white,
myofibrous-like component, and myxomatous (asterisk), hemorrhage, and tumor necrosis
foci. Several hard osteochondroid-like nodules were also palpable within this tumor
(arrow).

Transurethral resection of the urinary bladder tumor was performed. Pathological examination
led to a diagnosis of high-grade sarcoma composed of myofibrous differentiation, focal
myxomatous pattern, and a few chondroid changes with marked nuclear atypia and increased
mitotic figures (more than 10/10 high power field). Radical cystectomy was performed.
The patient currently remains well and prepares to undergo adjuvant chemotherapy.

Results

Macroscopically, the urinary bladder contained a nonencapsulated, huge, and lobular
mass, which was located in the left trigone and measured 14 × 13 × 7 cm. On its cut
surface, this tumor was composed of a predominant white, myofibrous-like component
(70%), with myxomatous (20%), hemorrhage, and tumor necrosis (7%) foci. Several hard
osteochondroid-like nodules were also palpable, and they measured around 3% of the
whole tumor lesion (Figure 1B, C, and 1D).

Discussion

Primary sarcomas of the urinary bladder are uncommon and mostly originate from muscle
such as rhabdomyosarcoma, which is dominant in children, or leiomyosarcoma, which
is dominant in adults. Other rare sarcomas documented in the literature include primary
osteosarcoma (31 cases) [1], malignant fibrous histiocytoma (30 cases) [2], primary angiosarcoma (15 cases) [3], and several cases of malignant mesenchymoma.

Malignant mesenchymoma is the rarest sarcoma of the urinary bladder, and it was defined
by Stout as a sarcoma comprising two or more unrelated differentiated tissue elements
other than a fibrosarcoma component. Our case presents five unrelated differentiated
tissues other than fibrosarcoma. To our knowledge, in the English-language medical
literature, only four cases of malignant mesenchymoma of the urinary bladder have
been previously reported [4-7]. The major clinical and pathological features of these cases and our case are summarized
in Table 2. The available data for malignant mesenchymoma of the urinary bladder show that it
predominantly occurs in male patients who are older than 40 years. The highest incidence
is in the eighth decade. The size of the tumor is often more than 10 cm, and an advanced
AJCC sarcoma stage is common when diagnosed.

Table 2. Major clinical and morphologic features of reported malignant mesenchymal tumor of
urinary bladder

Malignant mesenchymoma can occur at all locations in the body, including the retroperitoneum,
soft tissue of the lower limbs, heart [8], mediastinum [9], pleura [10], liver [11], orbit [12], bone [13], larynx [14], thyroid [15], testis [16], uterine [17], and urinary bladder [4-7]. Such tumors more frequently develop in the retroperitoneum and the soft tissue of
the lower limbs.

Several neoplasms remain that could qualify as malignant mesenchymoma according to
the definition, but these are frequently treated as distinct and separate entities,
such as malignant triton tumor, ectomesenchymoma, dedifferentiated liposarcoma, and
chondrosarcoma with a second differentiated component [18].

Malignant mesenchymoma appears to arise from a primitive mesenchymal cell with the
capacity for totipotent differentiation, but the histogenesis remains uncertain.

One should be careful when diagnosing malignant mesenchymoma, because some sarcomas
are easily combined with bone and chondroid metaplasia that could mimic this diagnosis.
The histological distinction between neoplastic and metaplastic bone is based on the
pattern of the deposited bone, the cytological features of the bone-forming cells,
and the cellular composition of the intratrabecular tissue. Metaplastic bone often
has a lamellar architecture, and it is usually organized around areas of hemorrhage
or portions of tumor. In contrast, the neoplastic osteosarcoma is usually surrounded
by deposited osteoid material (Figure 2C).

The prognosis of malignant mesenchymomas remains controversial. Malignant mesenchymomas
are commonly accepted as high-grade malignant neoplasms. Bradythe had reported two-
and three-year survival rates of 75% and 37%, respectively, in eight femoral and retroperitoneal
cases [19]. However, Newman and Fletcher suggested low-grade malignant behavior for malignant
mesenchymoma bases in six cases, four of which had less than five years of follow-up
[20]. Adachi reported that a patient aged under 40 years and the presence of a rhabdomyosarcomatous
component correspond to a poor prognosis, but there is no significant prognosis difference
with respect to gender, tumor site, tumor size, or MIB-1-labeling index [21].

Because of its extreme rarity, there are insufficient data to suggest the best modality
or combination of treatments for this condition [11,22,23]. Chemotherapy and radiotherapy were ineffective for the soft parts of the sarcoma,
including the malignant mesenchymoma, but the efficacy of chemotherapy with doxorubicin
plus ifosfamide and cyclophosphamide, vincristine, doxorubicin, and dacarbazine has
recently been reported. Thus, a multidisciplinary approach including surgery, radiotherapy,
and chemotherapy may be useful for these tumors [23].

Conclusions

In summary, malignant mesenchymoma is a rare tumor, and this is the fifth reported
case of a malignant mesenchymoma of the urinary bladder. Because of the limited experience
with this extremely rare tumor, there are insufficient data to suggest the optimal
management strategy and prognosis for malignant mesenchymoma of the urinary bladder.

Competing interests

The authors declare that they have no competing interests.

Authors' contributions

YFL drafted the manuscript. CPY carried out the immunohistochemical stains evaluation.
STW and MSD provide clinical information. HSL supervised this manuscript. All authors
read and approved the final manuscript.